As is known in the art, field emission displays (FEDs) are a type of cathode ray tube which include a cathode comprising a dielectric substrate on which an array of field emission elements are formed and a cathodoluminescent anode comprising a dielectric substrate on which an array of phosphor elements are formed. In assembly, the anode and cathode structures are bonded together so that the field emission elements face the phosphor elements and the enclosed structure is evacuated. In a color FED, each pixel includes phosphor elements of different colors. Typically, each set of a red, a green, and a blue phosphor element forms a pixel. Control electrodes control the flow of electrons between the field emission elements and respective pixels.
The voltage between the FED anode and cathode determines the brightness of the display. In particular, the higher the operating voltage, the brighter the display. Operating voltages between 4KV and 10KV are desirable.
The size and spacing of the phosphor elements, as well as the physical separation between the anode and cathode, affect the display resolution. In particular, the closer the anode and cathode, the higher the resolution. However, as such spacing gets smaller, the likelihood of arcing, particularly at high operating voltage levels, increases. Suitable anode to cathode separation for operating voltages of 4-10KV is on the order of 3-4 millimeters.
Spacers are sometimes positioned between the anode and the cathode in order to accurately and reliably maintain the small separation between these structures. In one such arrangement, the spacers are attached to the cathode substrate and, when the anode and cathode structures are bonded together and the tube is evacuated, the spacers come into contact with the anode.
One technique for forming a cathodoluminescent anode includes depositing a phosphor and photoresist slurry onto a dielectric substrate and then patterning the layer, such as with the use of photolithography, in order to provide the phosphor pixel elements. These steps may be repeated multiple times using different slurries in order to provide the different colors comprising the pixels. A layer of lacquer is applied over the phosphor elements in order to provide a relatively smooth surface for the subsequent application of a conductive layer, such as aluminum applied by evaporation. The structure is then baked at a temperature between 400.degree. C. and 450.degree. C. to remove any organics, including the lacquer and any photoresist, which causes the aluminum layer to be held onto the substrate and phosphor elements by electrostatic forces.
The force of the spacers against the aluminum layer can cause loose particles of aluminum to be generated. Loose particles can cause the anode and cathode to become electrically shorted together, thereby resulting in dead areas on the display. Such particles can also cause stray emissions resulting in illumination of areas of the display that should not be illuminated. Further, the loose particles can cause arcing which, in turn can cause more loose particles to be generated.